Valid Question; Not an Issue
Like many, I've followed this for years. The well-read but non-professional take is that devices similar to your self/GPS setting watch are not relevant to the aircraft's systems; in short, it sucks signals when it can find them, computes a little bit and does not blow. I have personal knowledge of several long-haul pilots who use similar devices without issue. Thus, the best advice is to use it, forget about it and *perhaps* be prepared to turn it off if anyone ever asks. I have to see this as a non-issue.
My personal use? I carry a hand-held transceiver and headset, simply because I like to know what's going on. Obviously, I keep the Tx function locked-out when I'm a pax and tend to keep the radio out of sight save the several frequency changes necessary. The headset used as SLC does NOT even have a mic and my radio provides a no-trx switch that I use. Said switch is bump-proof and use of the trx-disabled unit does NOT violate any rules. It provides more detail than does United's Chnl 9 and more often. It is also a nice "Second View" of what is happening with ATC, even when the flight and cabin crews LIE a lot. I never challenge them, but take some comfort in hearing original broadscasts fro ATC and company operations. Sorry, but flight crews (and cabin crews) do NOT always tell the truth. So why do I bother? 1) with the Trx function locked out, I am no threat to anyone, 2) In monitor-only mode, I hear a lot more detail than anyone of the airplane will ever explain and some listening often saves me 10-15 minutes on the tereminal end. And - without the antenna or mic, the modest unit rarely attracts any attention; I just listen. And know.